This invention relates to the field of intravascular catheters, and more particularly to a balloon catheters.
In percutaneous transluminal coronary angioplasty (PTCA) procedures a guiding catheter is advanced until the distal tip of the guiding catheter is seated in the ostium of a desired coronary artery. A guidewire, positioned within an inner lumen of an dilatation catheter, is first advanced out of the distal end of the guiding catheter into the patient""s coronary artery until the distal end of the guidewire crosses a lesion to be dilated. Then the dilatation catheter, having an inflatable balloon on the distal portion thereof, is advanced into the patient""s coronary anatomy over the previously introduced guidewire until the balloon of the dilatation catheter is properly positioned across the lesion. Once properly positioned, the dilatation balloon is inflated with liquid one or more times to a predetermined size at relatively high pressures (e.g. greater than 8 atmospheres) so that the stenosis is compressed against the arterial wall and the wall expanded to open up the passageway. Generally, the inflated diameter of the balloon is approximately the same diameter as the native diameter of the body lumen being dilated so as to complete the dilatation but not overexpand the artery wall. Substantial, uncontrolled expansion of the balloon against the vessel wall can cause trauma to the vessel wall. After the balloon is finally deflated, blood flow resumes through the dilated artery and the dilatation catheter can be removed therefrom.
In such angioplasty procedures, there may be restenosis of the artery, i.e. reformation of the arterial blockage, which necessitates either another angioplasty procedure, or some other method of repairing or strengthening the dilated area. To reduce the restenosis rate and to strengthen the dilated area, physicians frequently implant an intravascular prosthesis, generally called a stent, inside the artery at the site of the lesion. Stents may also be used to repair vessels having an intimal flap or dissection or to generally strengthen a weakened section of a vessel. Stents are usually delivered to a desired location within a coronary artery in a contracted condition on a balloon of a catheter which is similar in many respects to a balloon angioplasty catheter, and expanded to a larger diameter by expansion of the balloon. The balloon is deflated to remove the catheter and the stent left in place within the artery at the site of the dilated lesion. See for example, U.S. Pat. No. 5,507,768 (Lau et al.) and U.S. Pat. No. 5,458,615 (Klemm et al.), which are incorporated herein by reference. Thus, stents are used to open a stenosed vessel, and strengthen the dilated area by remaining inside the vessel.
At times, when either or both using a dilatation balloon catheter or a stent deployment catheter, the physician may have to exchange the catheter more than once due to the size of the catheter not being correct for the intended area of treatment.
Thus, what has been needed is a device that can provide information regarding the appropriate size of catheter. The present invention satisfies this and other needs.
The present invention is directed to a gauging system and method for using the same for determining the size of a lesion within a patient""s body prior to stenting the lesion.
In one embodiment the gauging system includes a catheter having an elongated shaft with proximal and distal ends, and an outer sheath formed of a compliant material and disposed about at least a portion of the catheter elongated shaft and being slidable over the same.
In another embodiment the gauging system includes a catheter having an elongated shaft with proximal and distal ends and inflation lumen extending within at least a portion of a distal shaft section to a location spaced proximally from the shaft distal end, a radially expandable member formed of a first compliant material mounted on the distal shaft section and having an interior chamber in fluid communication with the shaft inflation lumen, and an outer sheath formed of a second compliant material slidably disposed about at least a portion of the catheter elongated shaft and having a distal portion slidably disposed about the expandable member.
The outer sheath and the expandable member may be formed of the same or different compliant materials. The term xe2x80x9ccompliantxe2x80x9d as used herein refers to thermosetting and thermoplastic polymers which exhibit substantial stretching upon the application of tensile force. Additionally, compliant balloons transmit a greater portion of applied pressure before rupturing than non-compliant balloons. Additionally, the term xe2x80x9csame materialxe2x80x9d as used herein includes materials having the same chemical make up with the same or different physical properties (e.g., different durometers).
When the same material having the same chemical make up is used for forming the outer sheath and the expandable member, preferably, the outer sheath has a Shore durometer higher than the material for forming the expandable member. Alternatively, when the material forming the outer sheath and the expandable member have the same chemical make up and physical properties (e.g., Shore durometer), the wall thickness of the outer sheath is at least twice the wall thickness of the expandable member.
Suitable compliant balloon materials include, but are not limited to, elastomeric materials, such as elastomeric varieties of latex, silicone, polyurethane, polyolefin elastomers polyethylene, flexible polyvinyl chloride (PVC), ethylene vinyl acetate (EVA), ethylene methylacrylate (EMA), ethylene ethylacrylate (EEA), styrene butadiene styrene (SBS), ethylene propylene diene rubber (EPDM), polytetraflouroethylene (ePTFE), and Ultra high molecular weight polyethylene (UHMWPE). The presently preferred compliant material has an elongation at failure at room temperature of at least about 250% to about 650%, preferably from about 300% to about 400%, and a Shore durometer of about 45 A to about 75D, preferably about 60A to about 65D. Preferably, the balloon is a wingless balloon. Alternatively, when the balloon is preformed to include folds (or wings), the material forming the balloon should have excellent refold characteristics (such that the sheath can be placed over it), with preferably, a Shore durometer of about 60A to about 75D.
The presently preferred compliant material is a thermoplastic aromatic polyether polyurethane. More preferably, the compliant material has a softening temperature around body temperature (i.e., 37xc2x0 C.), thus, softening upon insertion into the body, resulting in improved performance. Additionally, balloons and sheaths formed of the present compliant materials are axially substantially non-compliant, i.e., have minimum axial growth as for example when the balloon is inflated, with the axial and radial size of the balloon deflating to the original pre-inflation size following inflation and deflation.